The present is a moment in time discernible as intermediate between past and future.

The present (or now) is the time that is associated with the events perceived directly and in the first time,[1] not as a recollection (perceived more than once) or a speculation (predicted, hypothesis, uncertain). It is a period of time between the past and the future, and can vary in meaning from being an instant to a day or longer. In radiocarbon dating, the "present" is defined as AD 1950.

It is sometimes represented as a hyperplane in space-time,[2] typically called "now", although modern physics demonstrates that such a hyperplane cannot be defined uniquely for observers in relative motion. The present may also be viewed as a duration (see specious present).[3][4]

There is no present or future, only the past, happening over and over again, now.

— Eugene O'Neill quotes

There's no present. There's only the immediate future and the recent past.

— George Carlin

You shouldn't chase after the past or place expectations on the future. What is past is left behind. The future is as yet unreached. Whatever quality is present you clearly see right there, right there.

The present is contrasted with the past and the future. Modern physics has not yet been able to explain the perceived aspect of 'the present' as 'eliminator of possibilities', that transfers future into past. Physical laws formally are valid at any point of time (classical or quantum mechanics) or even globally (general relativity), there isn't a concept of a present time in this context. A complicating factor is that whilst a given observer would describe 'the present' as a spatial structure with a zero-length time lapse, other observers would associate both time and space to this structure and therefore disagree on what constitutes 'the present'.

The direct experience of the present for each human is that it is what is here, now. Direct experience is of course subjective by definition yet, in this case, this same direct experience is true for all humans. For all of us, 'here' means 'where I am' and 'now' means 'when I am'. Thus, the common repeatable experience is that the present is inextricably linked to oneself.

In the time aspect, the conventional concept of 'now' is that it is some tiny point on a continuous timeline which separates past from future. It is not clear, however, that there is a universal timeline or whether, as relativity seems to indicate, the timeline is inextricably linked to the observer. Thus, is 'now' for one observer the same time as 'now' for another on a universal timeline, assuming a universal timeline exists? Adding to the confusion, in the physics view, there is no demonstrable reason why time should move in any one particular direction. The laws of physics simply are valid at any point in time; they describe events at 16:45 yesterday and events at 20:45 tomorrow. The idea that time moves isn't contained in these laws.

Adding substance to the supposition that the timeline view of 'now' may not hold the full picture, the qualities of 'now' or the 'present' in the human direct experience are very different from the qualities of past and future available through memory or anticipation. In the human direct experience, 'now' has a certain aliveness, reality and immediacy not present in our concepts of past and future. Indeed, any experience is always happening 'now', even a re-living of some past event. Thus, there is a deep philosophical case for saying that the present moment is all there ever is, and that temporal perception is, and only can be, this very moment.

When comparing time in places separated by great distances, the notion of present becomes more subjective. For example, we visually perceive stars to be where they were when the light now reaching our eyes was emitted, because even though light travels at approximately 300,000,000 metres per second (980,000,000 ft/s), it takes many years to reach us from distant sources. Thus, light travel time must be taken into account in such time comparisons.

In Patanjali Yoga Sutras the first sutra defines Yoga as 'NOW'. By 'Chitta Vrithhi nirodha' (restraining the thought-streams) the present can be experienced. The moment a person thinks, he is recalling his past experience. He will never know the present. Being conscious or being aware is the only way to know the present.

Buddhism and many of its associated paradigms emphasize the importance of living in the present moment — being fully aware of what is happening, and not dwelling on the past or worrying about the future.[7] This does not mean that they encourage hedonism, but merely that constant focus on one's current position in space and time (rather than future considerations, or past reminiscence) will aid one in relieving suffering. They teach that those who live in the present moment are the happiest.[8] A number of meditative techniques aim to help the practiser live in the present moment.

Christianity views God as being outside of time and, from the divine perspective past, present and future are actualized in the now of eternity. This trans-temporal conception of God has been proposed as a solution to the problem of divine foreknowledge (i.e. how can God know what we will do in the future without us being determined to do it) since at least Boethius.[9]Thomas Aquinas offers the metaphor of a watchman, representing God, standing on a height looking down on a valley to a road where past present and future, represented by the individuals and their actions strung out along its length, are all visible simultaneously to God.[10] Therefore, God's knowledge is not tied to any particular date.[11]

"The present" raises the difficult question: "How is it that all sentient beings experience now at the same time?"[12] There is no logical reason why this should be the case and no easy answer to the question. For example, say somebody named John is experiencing a great deal of pain. John's friend Sarah takes pity on John because of John's situation. The problem is: is it logical for Sarah to feel bad for John at present, when there is no way to prove that both John and Sarah experience the same temporal existence? (See also Solipsism and Philosophy of mind.)

A visualisation of the present (dark blue plane) and past and future light cones in 2D space.

The original intent of the diagram on the right was to portray a 3-dimensional object having access to the past, present, and future in the present moment (4th dimension).[clarification needed]

It follows fromAlbert Einstein's Special Theory of Relativity that there is no such thing as absolute simultaneity. When care is taken to operationalise "the present", it follows that the events that can be labeled as "simultaneous" with a given event, can not be in direct cause-effect relationship. Such collections of events are perceived differently by different observers. Instead, when focusing on "now" as the events perceived directly, not as a recollection or a speculation, for a given observer "now" takes the form of the observer's past light cone. The light cone of a given event is objectively defined as the collection of events in causal relationship to that event, but each event has a different associated light cone. One has to conclude that in relativistic models of physics there is no place for "the present" as an absolute element of reality. Einstein phrased this as: "People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion".[13]

"Today" signifies a "day" in a 24-hour interval to signify one's stance within the plane of time, this is contrary to "now", because "now" has no definite measure for its own duration. On the graph of Space-Time, the present can appear to be infinitely small, or account for a large portion of a sequence. In British culture the word "now" would also indicate " now in a minute " this is well known in popular culture around UK and US.

^Letter from Einstein to the family of his lifelong friend Michele Besso, after learning of his death, (March 1955) as quoted in Science and the Search for God: Disturbing the Universe (1979) by Freeman Dyson, Ch. 17, "A Distant Mirror", ; also quoted at-Einstein's God (NPR)